The invention relates to a finishing tool for viscous material known in the trade as a trowel. In the invention, the elements of the structure permit the trowel to be manufactured from materials that are different from those used heretofore in the art and which have properties that facilitate manufacture and use as a tool.
Trowels used in hand spreading and smoothing of viscous materials such as adhesives, plaster, and concrete are well known in the art, and are generally made of a flat blade member with a handle, the blade being modified in some cases for particular applications. Such trowels have typically been made of metal, which has many beneficial properties, but also has the disadvantages of complex manufacturing operations and susceptibility to corrosion.
One type of trowel in the art used for the measured spreading of viscous materials, such as an adhesive has a blade that has at least one notched or serrated edge with notch spacings that serve to measure the quantity being applied. One illustration of a serrated blade trowel is shown in U.S. Pat. No. 4,724,572. Another type of trowel in the art used for the finishing of plaster or concrete has a blade which in one portion is provided with a bend that facilitates edging of the material being finished. An illustration of a trowel with a finishing bend is shown in U.S. Pat. No. 4,737,097. The attachment and positioning of the handle of a trowel is of some importance. It is positioned relatively centrally of the blade with space for the hand, yet it must be fastened to the blade with sufficient retentive strength so as to withstand any mechanical advantage of forces applied at the edge of the blade in the course of the finishing or spreading operation. The handle, further, must be retained on the blade in such a manner that the side of the blade that is used in finishing does not mar the smoothness to be achieved--which could occur if the retention means for the handle extended through the blade.
In the 4,724,572 patent, the blade is provided with an opening and the handle fits flush in the opening, being retained by tangs. This requires a special cooperative structure between handle and blade with material and shaping limitations.
In the 4,737,097 patent, the handle is fastened to a flat plate that is in turn bonded to one side of the blade.
Heretofore in the art, the criteria for the tool have commonly been met using metal as a material. However, as the art progresses it is becoming advantageous to use materials other than metals. For example, plastic material can be judiciously utilized enable achievement of a light weight tool, greater ease in manufacturing and shaping, as well as providing corrosion resistance, in comparison with metals.
U.S. Patent No. 4,316,302 discloses a one-piece plastic trowel. The handle of this trowel includes integrally molded portions overlapping the top of the blade. The junction of the handle with the blade is a region of extremely high stress, and a region where high strength is necessary. As is well known, it is difficult to produce a molded plastic article having large concentrated masses of material without post-molding shrinkage. Accordingly, the strength of the junction of the blade and handle in an integrally molded tool is limited by the amount of material which can be placed at this critical location.